The invention relates to an optical system for a tiltable lens barrel of a microscope or the like. More particularly, it relates to an optical system for use with a microscope, an optical measuring instrument or the like that is provided with an observation lens barrel which is variable in its axial tilt angle.
It is extremely desirable in a microscope to see an erect image and to make an axial tilt angle of an observation lens barrel variable. It should be noted that prior art lens barrels which have axes variable in tilt angle are few, found merely occasionally in low-grade microscopes and rarely, if ever, in high-grade ones.
Even though it is rarely the case that an observation lens barrel is variable in its axial tilt angle, a known method for making a lens barrel variable in its axial tilt angle is illustrated in FIG. 1. The arrangement of this figure makes an observation lens barrel axis variable in tilt angle and allows a total reflecting mirror 2 disposed on an optical axis of an objective 1 to rotate. Specifically, the total reflecting mirror 2 which is disposed on an optical axis of objective 1 and which directs an observation optical image toward an eyepiece lens 3 in an observation lens barrel 4 is built into the lens barrel 4 so as to be variable in its tilt angle .theta..sub.1, the latter also being variable in its axial tilt angle .theta..sub.2. In such an arrangement, when a tilt angle .theta..sub.2 of lens barrel 4 changes total reflecting mirror 2 also is correspondingly allowed to change in its tilt angle .theta..sub.1.
According to the above described method, an observation lens barrel can be comparatively simply changed in its axial tilt angle. However, it is to be noted that total reflecting mirror 2 must be made considerably larger so that a light beam passing through it is not vignetted, thus requiring a lens barrel which as a whole must be of a disadvantageously large size.